The United States and all other modern industrial economies experience significant swings in economic activity. In some years, most industries are booming and unemployment is low; in other years, most industries are operating well below capacity and unemployment is high. Periods of economic prosperity are typically called expansions or booms; periods of economic decline are called recessions or depressions. The combination of expansions and recessions, the ebb and flow of economic activity, is called the business cycle.
Business cycles as we know them today were codified and analyzed by Arthur Burns and Wesley Mitchell in their 1946 book Measuring Business Cycles. One of Burns and Mitchell’s key insights was that many economic indicators move together. During an expansion, not only does output rise, but also employment rises and unemployment falls. New construction also typically increases, and inflation may rise if the expansion is particularly brisk. Conversely, during a recession, the output of goods and services declines, employment falls, and unemployment rises; new construction also declines. In the era before World War II, prices also typically fell during a recession (i.e., inflation was negative); since the 1950s prices have continued to rise during downturns, though more slowly than during expansions (i.e., the rate of inflation falls). Burns and Mitchell defined a recession as a period when a broad range of economic indicators falls for a sustained period, roughly at least half a year.
Business cycles are dated according to when the direction of economic activity changes. The peak of the cycle refers to the last month before several key economic indicators—such as employment, output, and retail sales— begin to fall. The trough of the cycle refers to the last month before the same economic indicators begin to rise. Because key economic indicators often change direction at slightly different times, the dating of peaks and troughs is necessarily somewhat subjective. The National Bureau of Economic Research (NBER) is an independent research institution that dates the peaks and troughs of U.S. business cycles. Table 1 shows the NBER monthly dates for peaks and troughs of U.S. business cycles since 1890. Recent research has shown that the NBER’s reference dates for the period before World War I are not truly comparable with those for the modern era because they were determined using different methods and data. Figure 1 shows the unemployment rate since 1948, with periods that the NBER classifies as recessions shaded in gray. Clearly, a key feature of recessions is that they are times of rising unemployment.
Link to full article in the EconLib Concise Encyclopedia of Economics